Masonry Magazine August 1973 Page. 19
NCMA-TEK
An Information series from National Concrete Masonry Association
Concrete Masonry
Sizes, Shapes, Forms, and Functions
Introduction
The versatility of concrete masonry is vividly demonstrated by the range of sizes and shapes of units being manufactured today. Forty years ago, inventory of a typical block manufacturing plant consisted of less than 30 different sizes. Today, this figure exceeds 100 and the total number of different sizes, shapes and types manufactured across the country is well over 700. As well as reflecting the mounting variety of applications of concrete masonry in todays construction, this increase results from the ability of the manufacturer to provide the units necessary for the many functions that may be required. Units are made in sizes which range from one inch in thickness and in lengths up to twenty four inches; they are solid or hollow and are made with dense and lightweight aggregates so that the concrete of which the units are formed may have controlled density from less than 70 lb./cu. ft. to more than 140 lbs. per cubic foot, and average compressive strength up to 7500 psi.
Concerning sizes and shapes, a group of units has evolved over the years which provide sufficient versatility to handle most andle most wall projects. These are generally referred to as "standard" where reinforced masonry construction is widely used but may be considered as special units where this type of construction is scarce. The name designating various units has been fairly well standardized and usually relates to the function in the wall. Several such units are shown in Figure 1 where the configuration implies the use for which the block is intended.
After modular standards were introduced the concrete masonry industry adapted production to these standards and today all plants can furnish standard units of a nominal size which will fit the 4" module. The nominal dimension includes 3/8" allowed for the thickness of a standard mortar joint, so the actual dimensions of the well known 8" x 8" x 16" unit are manufactured as 7-5/8" x 7-5/8" x 15-5/8".
ASTM Specifications permit a maximum variation in overall dimensions (length, width and height) of plus or minus 1/8" from the actual dimensions specified by the manufacturer. It is the usual practice, however, to manufacture the units within a tolerance of plus or minus 1/16".
TABLE 1
Minimum Thickness of Face Shell and Webs
(Applies to ASTM C 90-70 Only)
| Nominal Width (W) of Units, in. | Face-Shell Thickness (FST) min, in. | Webs,* min, in. | Web Thickness (WT) Equivalent Web Thickness, min, in./lineal ft.** |
|---|---|---|---|
| 3 and 4 | % | % | 1% |
| 6 | 1 | 1 | 2% |
| 8 | 1% | 1 | 2% |
| 10 | 1% | 1% | 2% |
| 12 | 1%*** | 1% | 2% |
| | 1%**** | | |
* Average of measurements on 3 units taken at the thinnest point.
** Sum of the measured thickness of all webs in the unit, multiplied by 12. and divided by the length of the unit.
***The face-shell thickness (FST) is applicable where allowable design load is reduced in proportion to the reduction in thickness from basic face-shell thicknesses shown.